I am going to preface that this post is a result of an article I read here:
Underwater lights: whiskey tango foxtrot?! | Navagear.com
I normally do not post to those kind of blogs (but highly recommend adding it to your "must read resources, esp if in the PNW).
I actually see value in underwater lights:
Greater visibility when mooring in a crowded anchorage. It is also less obtrusive than say running your spreader lights. Places like Port Madison, where even with a full moon you can almost have to transit under radar - to avoid hitting a moored / anchored boat.
At night, when in shallow areas gives you a visual of what you are dealing with. Rudimentary things like checking rudder position, etc...
Having to dive the boat beyond normal daylight, it is basically a hands free work light.
Lastly, if you have a bunch of "party guests" - someone goes over etc, I can see it as a tool for the person getting back to the boat in pitch black.
What are your thoughts? Do you have them? Mock them? Way better discussion than solar sticks versus light sabers...